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Merge pull request #2159 from MerryMage/cxxrtl-mul

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cxxrtl: Implement chunk-wise multiplication
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whitequark 2020-06-15 06:08:17 +00:00 • committed by GitHub
commit 334ec5fa0a
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1 changed files with 22 additions and 17 deletions
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39
backends/cxxrtl/cxxrtl.h
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@ -66,6 +66,7 @@ namespace cxxrtl {
// Therefore, using relatively wide chunks and clearing the high bits explicitly and only when we know they may be
// clobbered results in simpler generated code.
typedef uint32_t chunk_t;
typedef uint64_t wide_chunk_t;
template<typename T>
struct chunk_traits {
@ -454,6 +455,24 @@ struct value : public expr_base<value<Bits>> {
bool overflow = (is_neg() == !other.is_neg()) && (is_neg() != result.is_neg());
return result.is_neg() ^ overflow; // a.scmp(b) ≡ a s< b
}
template<size_t ResultBits>
value<ResultBits> mul(const value<Bits> &other) const {
value<ResultBits> result;
wide_chunk_t wide_result[result.chunks + 1] = {};
for (size_t n = 0; n < chunks; n++) {
for (size_t m = 0; m < chunks && n + m < result.chunks; m++) {
wide_result[n + m] += wide_chunk_t(data[n]) * wide_chunk_t(other.data[m]);
wide_result[n + m + 1] += wide_result[n + m] >> chunk::bits;
wide_result[n + m] &= chunk::mask;
}
}
for (size_t n = 0; n < result.chunks; n++) {
result.data[n] = wide_result[n];
}
result.data[result.chunks - 1] &= result.msb_mask;
return result;
}
};
// Expression template for a slice, usable as lvalue or rvalue, and composable with other expression templates here.
@ -1306,28 +1325,14 @@ value<BitsY> sub_ss(const value<BitsA> &a, const value<BitsB> &b) {
template<size_t BitsY, size_t BitsA, size_t BitsB>
CXXRTL_ALWAYS_INLINE
value<BitsY> mul_uu(const value<BitsA> &a, const value<BitsB> &b) {
value<BitsY> product;
value<BitsY> multiplicand = a.template zcast<BitsY>();
const value<BitsB> &multiplier = b;
uint32_t multiplicand_shift = 0;
for (size_t step = 0; step < BitsB; step++) {
if (multiplier.bit(step)) {
multiplicand = multiplicand.shl(value<32> { multiplicand_shift });
product = product.add(multiplicand);
multiplicand_shift = 0;
}
multiplicand_shift++;
}
return product;
constexpr size_t BitsM = BitsA >= BitsB ? BitsA : BitsB;
return a.template zcast<BitsM>().template mul<BitsY>(b.template zcast<BitsM>());
}
template<size_t BitsY, size_t BitsA, size_t BitsB>
CXXRTL_ALWAYS_INLINE
value<BitsY> mul_ss(const value<BitsA> &a, const value<BitsB> &b) {
value<BitsB + 1> ub = b.template sext<BitsB + 1>();
if (ub.is_neg()) ub = ub.neg();
value<BitsY> y = mul_uu<BitsY>(a.template scast<BitsY>(), ub);
return b.is_neg() ? y.neg() : y;
return a.template scast<BitsY>().template mul<BitsY>(b.template scast<BitsY>());
}
template<size_t BitsY, size_t BitsA, size_t BitsB>